Traditionally, MOSFETs (metal oxide semiconductor field effect transistors) have been implemented with a single control electrode or gate on a planar substrate. The gate is placed between a source and drain electrode and functions to create a channel controlling the amount of current between the source and drain electrodes. Because there is only a single gate electrode to control the channel, the transistor may exhibit undesirable characteristics. For example, the planar transistor may suffer from certain short channel effects, where the drain electrode has an unwanted effect on the channel resulting in excessive leakage current.
A vertical double gate transistor design, also known as a finFET, has been proposed to eliminate some of the problems with single gate planar transistor design. In a vertical double gate transistor design, the channel consists of a pillar or slab, (the fin in finFET) that is oriented perpendicular to the plane of a substrate, but a line connecting the source and drain is parallel to the substrate plane. A gate material such as polysilicon or metal is formed on both sides of the fin. The double gate arrangement increases electrostatic coupling between the gates and the channel relative to the single gate design. Also, drive current is improved with decreased leakage. Because of the performance advantages offered by the use of vertical double gate transistors, it would be desirable to convert existing integrated circuit designs that use planar transistors. However, extensive layout/design changes may be necessary when converting a design using planar transistors to a design using vertical double gate transistors. Therefore, there is a need for a way to easily convert a planar transistor design to a vertical double gate transistor design.